Know what, I'm not caring if this has already been done, this is wonderful. Because:

1) For the 'honest' people who bring the wallet back, they immediately get an overwhelming reward - the positive approval of a crowd of their *peers* - strangers on the same team, and get a bottle of coke thrust into their hands, "go on, drink it, now, quick, so your brain makes a concrete link between this huge endorphin overload and the taste of this bottle."

2) For the crowd at the match, they get to see that they're on the right team, full of honest people, rewarded for their honesty by wellbeing and Coke - conflated into one and the same by the wonders of positive reinforcement.

3) This is a psychologist's wet dream: a superb example of social engineering and manipulation.

would NEVER EVER had worked in Istanbul Galatasaray vs Fenerbahce!!!!
NEVER
They would've pissed in the wallet. at the store. in front of all people. and everybody would be proud of the pisser pissing on the enemies ticket!